The invention generally relates to semiconductor device fabrication and, it relates, more particularly, to a method for producing a recessed or sunken oxide in semiconductor device processes.
In bipolar high-frequency transistors of silicon semiconductor material, the capacitance of the bonding pads reduces the effective high-frequency response of the bipolar transistors. In order to decrease the capacitance of the connecting pads, either the bonding pads must be kept small which hinders automatic assembly of the bipolar high-frequency transistor chips when mounting these chips in the housing of these bipolar high-frequency transistors; or the oxide which lies on the semiconductor surface of the bipolar transistors between a bonding pad, for example of an emitter or a base and the collector, can be made thick which, however, in particular in the utilization of contact exposure for structuring the oxide on the semiconductor surface, makes creating an image of fine structures impossible.
Until now in bipolar high-frequency transistors of silicon, primarily small bonding pads were fabricated since a thickening of the oxide on the semiconductor surface produces a depression of the base basin which interferes, in particular in contact exposures for structuring the oxide. In order to remedy this interference, the oxide could be sunk on the semiconductor surface. Methods used up to now for sinking the oxide have either had a negative influence on other high-frequency parameters, for example the LOCOS technology, or they are technologically very complex, for example generating an oxide on the semiconductor surface of porous silicon.